I would like to get an app so I can sync some folders between my PC, netbook, external HDD. Can anyone give me a suggestion?

Thanks!

You can do it on the net by using Dropbox. 2Gb of free space. You install a small client application on both your PC and netbook. Then, It's just a question of dragging and dropping your files in the Dropbox folder.

Or you can use Microsoft SyncToy 2.0. Very basic application to synchronize between 2 folders. I have never tried it over a LAN though.